Method for producing tri-calcium phosphate

ABSTRACT

A method for producing tri-calcium phosphate admixes water, hydrated lime, and phosphoric acid in a reaction vessel to form a tri-calcium phosphate slurry. The slurry is then placed in physical contact with heated air through a spray head to evaporate water from the slurry. The preferred embodiment of the method utilizes an agitated air dryer.

CROSS REFERENCE TO RELATED APPLICATION

This continuation patent application claims priority from thenon-provisional application having Ser. No. 10/950,043 and filed on Sep.25, 2004, which claims priority from a provisional application havingSer. No. 60/505,397 and filed on Sep. 25, 2003 and which claims priorityfrom a provisional application having Ser. No. 60/505,397 and filed onDec. 4, 2003.

BACKGROUND OF THE INVENTION

This invention generally relates to tri-calcium phosphate production.More specifically, the present invention utilizes a production methodwith a spray head in combination with an agitated air dryer system.

Tri-calcium phosphate is the generic name for precipitated calciumhydroxyapatite. High-quality food-grade tri-calcium phosphate (“TCP”) isused as a calcium supplement in products such as cereals, bakery mixes,dry gravy mixes, spice blends, flours, beverages, animal foods andpharmaceuticals. TCP is also used as an anti-caking agent in saltsubstitutes, dry beverage mixes, dry soup mixes, dry gravy mixes, spiceblends and other hydroscopic food products that require flowconditioning. TCP also serves as a dispersant, a suspension agent forpolymerization of styrene, and a ceramic coloring agent.

Currently, TCP slurries are produced by admixing water, hydrated calciumor lime (CaOH), and phosphoric acid in a stainless steel reaction vessel7 in FIG. 1. A small amount of acetic acid is also added to control theviscosity of the slurry during the reaction and for passage through asurge tank 8. The slurry produced generally has a weight ratio of 72%water and 28% solid TCP. To produce a marketable TCP product, the slurrymust be dried to remove the moisture.

The industry standard for removing the moisture is drying the slurryusing a combination of steam heated double drum dryers, gas fired flashdryers 12, and air conveyance in FIG. 2. More specifically, drying TCPslurry by spreading it over a steam heated 11 double drum dryer 10 hasmuch inefficiency. The granular characteristics, density and moisturecontent for different marketable TCP products are determined in thedrying process. While the prior art drying techniques produce marketableTCP products, several drawbacks make these techniques less desirable.First, the prior art drying systems utilize a large amount of energy tooperate. Approximately 3,750 BTU (British Thermal Units) are required todry enough slurry to produce one pound of TCP at 2% moisture. The doubledrum dryer 10 employed has a small production capacity which increasesproduction costs. The drums have a capacity of approximately 800 lb to900 lb per hour. Finally, the double drum drying system generatesexcessive dust as the dried TCP is scraped from the drums and is droppedinto conveyors. The finer particles become airborne and drift onto thesurface of the dryer frame, and eventually onto the floor beneath thedryer. This finer material must be collected and disposed of as waste.

Therefore, an efficient TCP production method is needed that utilizesless water and energy for drying TCP to meet commercial needs.

SUMMARY OF THE INVENTION

The present invention is a method for producing tri-calcium phosphate.The method admixes water, hydrated lime, ascetic acid, and phosphoricacid in a reaction vessel to form a tri-calcium phosphate slurry, andthen places the slurry in physical contact with air at a temperaturesufficient to evaporate the water in the slurry.

The TCP slurry mixes with previously dried TCP (0%-2% moisture) toobtain a blended TCP product that has approximately 30% moisturecontent. This blend then feeds into an agitated air dryer (AGA) asmanufactured by International Technology Systems, Inc. of Wisconsin.

The moisture in the blended TCP evaporates in the AGA dryer by aturbulent stream of heated air. The present invention resulted fromdifferent locations of slurry sprays relative to the dryer and varioustypes and amounts of insulation placed upon the burner housing and thedryer itself. The air temperature at the inlet 5 a of the dryer 5 willvary between 550° F. and 650° F. The air temperature at the outlet 5 bof the dryer 5 will vary between 190° F. and 210° F. The hot moist airand dried product exit the dryer into a bag house B as in FIGS. 3, 4.The dry product drops to the bottom of the bag house where it splitsinto two product streams. One stream of dried TCP goes to packagingequipment 9 and along a packaging conveyor 9 a. Another stream ofproduct returns to the mixing equipment where it re-blends with the TCPslurry 6.

The hot moist air exits through the top of the bag house after passingthrough fabric bags. The fabric bags operate similar to the bags in avacuum cleaner. The fabric bags allow the hot air to pass through, butnot the fine, airborne TCP particles. This system keeps all the TCPcontained and eliminates waste.

The AGA drying system uses approximately 1,500 BTU to produce one poundof TCP product with 2% moisture. This system requires about 40% of theenergy used by the double drum drying system 10. The present inventionproduces approximately 1,650 lb/hr of finished TCP. Furthermore, thetemperature, turbulence and velocity of the air stream in the AGA dryingsystem can be readily adjusted to produce various granulations anddensities of the TCP to meet the specific requirements of a variety ofproducts.

Numerous objects, features and advantages of the present invention willbe readily apparent to those of ordinary skill in the art upon a readingof the following detailed description of the presently preferred, butnonetheless illustrative, embodiment of the present invention when takenin conjunction with the accompanying drawings. Before explaining thecurrent embodiment of the invention in detail, it is to be understoodthat the invention is not limited in its application to the details ofconstruction and to the arrangements of the components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced and carried out invarious ways. Also, the phraseology and terminology employed herein arefor the purpose of description and should not be regarded as limiting.

One object of the present invention is to provide a new and improvedmethod for producing tri-calcium phosphate.

Another object of the present invention is to combine the advantages ofa spray dryer and an agitated air dryer.

Another object is to provide a method for producing tri-calciumphosphate that reduces waste of TCP by containing particulate TCP withinthe equipment.

Another object is to provide a method for producing tri-calciumphosphate that uses 40% of the energy of prior art methods to operate.

A still further object is to provide a method for producing tri-calciumphosphate that readily provides TCP of various granulations anddensities.

These together with other objects of the invention, along with thevarious features of novelty that characterize the invention, are pointedout with particularity in the claims annexed to and forming a part ofthis disclosure. For a better understanding of the invention, itsoperating advantages and the specific objects attained by its uses,reference should be had to the accompanying drawings and descriptivematter in which there is illustrated a preferred embodiment of theinvention.

Variations and modifications to the subject matter of this invention mayoccur to those skilled in the art upon review of the development asdescribed herein. Such variations, if within the spirit of thisdevelopment, are intended to be encompassed within the scope of theinvention as described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating the preferred embodiment of themethod of the present invention;

FIG. 2 is a flow chart illustrating the prior art method for producingtri-calcium phosphate;

FIG. 3 is top view of the preferred embodiment of the present inventionin a production environment; and,

FIG. 4 is a side view of the preferred embodiment of the presentinvention in a production environment.

The same reference numerals refer to the same parts throughout thevarious figures.

DETAILED DESCRIPTION

A new and useful method for producing commercial tri-calcium phosphate,or TCP, utilizes less water and energy than current methods. TCP has amolecular weight of 502 and has the following chemical formula:Ca₅(PO₄)₃(OH). The processes of the present invention produce a TCPproduct with less energy and less waste than the current methods.According to the method of the present invention in FIG. 1, water 1,hydrated lime 2, related ingredients such as acetic acid 4, andphosphoric acid 3 are admixed in a reaction vessel 7 to form atri-calcium phosphate slurry 6. The resultant slurry 6 has approximately72% water and 28% by weight of solid TCP. The slurry 6 then physicallycontacts air to remove the moisture from the slurry 6. To remove themoisture, the air temperature must reach the evaporation point of themoisture in the slurry 6. The heat of the chemical reaction iscontrolled to produce TCP having certain characteristics, such as fineparticle or powdery form.

In the preferred method of the invention, an agitated air or AGA system5 dries the TCP slurry 6. Suitable AGA systems 5 may be obtained fromInternational Technologies Systems, Inc. The agitated air system 5utilizes a dispersion drum and paddles to separate the TCP slurry 6 intosmall particles so that a fast moving stream of hot air may remove themoisture in the slurry 6 through evaporation. In the preferred method ofthe invention, TCP slurry 6 is fed through a spray head 5 c directlyupon the dispersion drum of the dryer 5. In an alternate method, thedispersion drum has paddles. In addition, the AGA system 5 has aproduction capacity of about 1,300 lb to about 2,000 lb per hour, versusabout 800 lb to about 900 lb per hour with the prior art dryers.Further, the AGA system 5 works more efficiently at lower moisturelevels than current methods. A double drum drying system 10 of the priorart, as in FIG. 2, requires high moisture content TCP to distribute TCPevenly upon the surface of the drums. The granular characteristics,density and moisture for different marketable TCP products aredetermined largely by the dryer shaft speed, air volume and airtemperature. Using the AGA system 5, negative air pressure moves the TCPslurry 6 through the system. This retains the product within the dryingequipment. Dust from the production of the TCP remains and returns tothe production line P using bag houses B.

Turning to FIG. 3, the method of the present invention takes form in aproduction environment. Components are mixed and a slurry forms in thetank 7. From the tank 7, slurry 6 is piped to an agitated air dryer 5.The dryer 5 includes one or more spray heads 5 c ahead of the inlet 5 a.As moisture departs the slurry 6, the particulate TCP exits the dryerthrough the outlet 5 b and proceeds into the production line P. Theproduction line P leads to a baghouse B also connected to a fan F. Aspreviously described, the baghouse B captures particulate TCP, releasesair, and collects TCP in bulk. A conveyor 9 a takes the bulk TCP intothe packaging equipment 9 for further handling such as screening.

FIG. 4 shows the combination of the dryer and the spray head arrangedfor production of TCP. As in FIG. 3, slurry 6 departs the tank 7 andenters the dryer 5. Exiting the dryer 5, the TCP proceeds to thebaghouse B through the production line P. To heat the air used in thedryer 5, a burner N mounts upon the dryer 5 and communicates heated airfor evaporating moisture from the TCP. The dryer 5 admits the slurry 6at the inlet 5 a. Inside of the inlet 5 a, one or more spray heads 5 cdisperse the slurry 6 under pressure upon the drums within the agitatedair dryer 5. As the moisture content declines, the particulate TCP isevacuated from the dryer 5 through the outlet 5 b and sent into theproduction line P.

The TCP produced using the method of the present invention may be usedin various products, including but not limited to, foods, ceramics, bonemeal, and beverages. The TCP products may also be used in polystyrenemanufacturing. From the aforementioned description, a method forproducing tri-calcium phosphate has been described. The productionmethod is uniquely capable of drying a TCP slurry.

As such, those skilled in the art will appreciate that the conception,upon which this disclosure is based, may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. Therefore, the claimsinclude such equivalent constructions insofar as they do not depart fromthe spirit and the scope of the present invention.

It is to be understood that while certain embodiments of the inventionare described and illustrated herein, the invention is not to be limitedto the specific form or arrangement described and shown herein. It willbe apparent to those skilled in the art that various changes may be madewithout departing from the scope and spirit of the invention, and theinvention is not to be considered limited to what is shown and describedherein.

1. A method of producing dry marketable hydroxyapatite, commonly knownas tri-calcium phosphate, combined from ingredients including water,hydrated lime, phosphoric acid, and acetic acid, comprising: forming aslurry from said ingredients including approximately 72% water by weightand approximately 28% tri-calcium phosphate by weight wherein saidtri-calcium phosphate attains an initial moisture content ofapproximately 30%; adding to said slurry less than 2% by weight aceticacid for controlling the viscosity of said slurry during the reaction ofsaid ingredients during mixing of said slurry; placing said slurrywithin heated air produced by an agitated air system having an agitatedair dryer with an inlet and an outlet and at least one spray headlocated between said inlet and said outlet, said at least one spray headdirectly applying said slurry within an agitated heated air streamwithin the air dryer; maintaining the temperature at said inlet of theair dryer of approximately 550° F. to approximately 650° F., andmaintaining the temperature of said air outlet at approximately 190° F.to approximately 210° F.; using negative air pressure within saidagitated air system to move said slurry through said air dryer and todirect said slurry through said at least one spray head in contact withthe stream of heated air to evaporate water from said slurry to producea tri-calcium phosphate having a moisture content less thanapproximately 2%; and, said method producing tri-calcium phosphate at arate of at least 1,300 pounds per hour and at less than 1,500 Btu usedper pound.
 2. The method of claim 1 further comprising: dividing saidtri-calcium phosphate produced by said method into two portions;recycling one of said portions into the step of forming said slurry;and, packaging the other of said portions for delivery.
 3. The method ofclaim 1 further comprising: said air dryer having at least one paddle.4. The method of claim 1 further comprising: forming a slurry includingapproximately 72% by weight water, approximately 11% by weight hydratedlime, approximately 16% by weight phosphoric acid, and less than 1% byweight acetic acid.
 5. A method of producing dry marketablehydroxyapatite, commonly known as tri-calcium phosphate, combined fromingredients including water, hydrated lime, and phosphoric acid,comprising: forming a slurry from said ingredients includingapproximately 72% water by weight, and approximately 28% hydrated limeand phosphoric acid by weight, said slurry including tri-calciumphosphate of an initial moisture content of approximately 30%; placingthe slurry in contact with heated air produced by an agitated air systemhaving an agitated air dryer with an inlet and an outlet and at leastone spray head between said inlet and said outlet, said at least onespray head directly applying said slurry within said agitated heated airstream within the air dryer; maintaining the inlet of the air dryer at atemperature of approximately 550° F. to approximately 650° F., andmaintaining the outlet of the air dryer at a temperature ofapproximately 190° F. to approximately 210° F.; using negative airpressure within said agitated air dryer to move said slurry through saiddryer and directing said slurry through said at least one spray head incontact with the stream of heated air to evaporate water from saidslurry to produce a tri-calcium phosphate having a moisture content ofless than approximately 2%; splitting said tri-calcium phosphateproduced by said method into two portions, returning one of saidportions into said slurry, and packaging the other of said portions fordelivery; and, said method producing tri-calcium phosphate, at a rate ofat least 1,300 pounds per hour and with less than 1,500 Btu used perpound.
 6. The method of claim 5 further comprising: said forming saidslurry including less than 2% by weight acetic acid.
 7. The method ofclaim 5 further comprising said air dryer having at least one paddle. 8.The method of claim 5 further comprising: said forming said slurryincluding hydrated lime and phosphoric acid in similar proportions byweight.
 9. The method of claim 5 further comprising: said forming saidslurry including approximately 11% by weight hydrated lime,approximately 16% by weight phosphoric acid, and less than 1% by weightacetic acid.
 10. A method of producing dry marketable hydroxyapatiteCa₅(PO₄)₃(OH), also known in trade as tri-calcium phosphate, comprising:forming a slurry including approximately 72% by weight water,approximately 11% by weight hydrated lime, approximately 16% by weightphosphoric acid, and approximately 1% by weight acetic acid forcontrolling the viscosity of said slurry during the reaction of saidingredients during mixing of said slurry, wherein said slurry containstri-calcium phosphate of a moisture content of approximately 30%;placing said slurry within heated air produced by an agitated air systemhaving an agitated air dryer with an inlet and an outlet, at least onepaddle, and at least one spray head located between said inlet and saidoutlet, said at least one spray head directly applying said slurrywithin an agitated heated air stream within the air dryer; maintainingthe temperature at said inlet of the air dryer of approximately 550° F.to approximately 650° F., and maintaining the temperature of said airoutlet at approximately 190° F. to approximately 210° F.; using negativeair pressure within said agitated air system to move said slurry throughsaid air dryer and to direct said slurry through said at least one sprayhead in contact with the stream of heated air to evaporate water fromsaid slurry to produce tri-calcium phosphate exiting said system havinga moisture content less than approximately 2%; said method producingtri-calcium phosphate at a rate of at least 1,300 pounds per hour and atless than 1,500 Btu used per pound; and, dividing said tri-calciumphosphate produced by said method into two portions wherein one of saidportions is recycled into the step of forming said slurry and whereinthe other of said portions is packaged for delivery.